Thermoplastic splint or cast

ABSTRACT

Polydiene sheet material useful as a body supporting member such as a cast or splint, heat softenable at a higher than body temperature, but slowly recrystallizable or hardenable below about 40° C., treated by distributing throughout the substance small pores, perforations or surface irregularities as by foaming all or only one surface portion of the sheet material, particularly texturing, knurling, pocking or cratering the surface to be placed adjacent to the body member to be encased to allow moisture and/or air transfer away from the enclosed body surface.

This invention is a continuation-in-part of my copending application,Ser. No. 3,474, filed Jan. 16, 1970, and now U.S. Pat. No. 3,809,600, inturn a continuation-in-part of my copending application, Ser. No.683,016, filed Nov. 4, 1967, now U.S. Pat. No. 3,490,444.

This invention relates to improved processes for forming body supportingcasts or splints from thermoplastic sheets and tapes which are moldableto desired body supporting shape when softened by heat above thecritical crystalline melting point and held there for a sufficient timeto become moldably soft, the plastic returning to its crystallinehardness upon cooling, the plastics hereof upon softening developing ahysteresis which allows the plastic to pass through the crystallinemelting point upon cooling to a temperature well below that point suchas below a comfortable body temperature to remain soft and pliable,thereby allowing easy application to the body at a comfortabletemperature. The softened plastic then hardens in a reasonable time atthe lower temperature to set to a hard crystalline polymer substance inbody support form.

More particularly, this invention is directed to using certainpolydienes, typically transpolyisoprene or transpolychlorene, as plasticsubstances in sheet or tape form, or other suitable form for use as abody supporting cast or splint, by heating the polymer well above itscrystalline transition point such as above 65° C. and, more practically,usually up to the boiling point of water for a period long enough tothoroughly soften the plastic material and to overcome by heating allcrystalline portions of the plastic body thoroughly and then cooling theheated plastic down to a comfortable body temperature such as about 45°C. or less, and then applying the softened plastic material to the bodymember to be protected as a cast or splint, holding the encased bodymember for an additional period until the splint material hardens andsets by crystallization.

This invention further provides surface irregularities, perforations ora porous texture upon at least the surface upon the sheet materialadapted to lie adjacent to the body part to be encased by the sheath orsplint which is made porous.

In a prior invention, Canadian Pat. No. 746,291, dated Nov. 15, 1966,whose substance is here incorporated by reference, certain polydienes,typically transpolyisoprene such as natural balata essentially freed ofnatural resins by precipitation, its synthetic form transpolyisoprene,as well as low temperature polymerized polychloroprene are shown to beuseful plastic substances in sheet or tape form for forming body membersupporting casts and splints. It was proposed in my prior patent thatthese selected polymers be heated at a temperature usually exceedingabout 65° C. and up to about 110° C., whereby they become soft,self-coherent and pliable, sufficient to be deformed and shaped as acast or splint about a body member broken or deformed or otherwiserequiring mechanical support or protection.

It was believed that similar to any normal plastic, these plasticsubstances would merely soften with heat and crystallize with cooling asillustrated in FIG. 9 below. For that reason, while it is indicated theproduct could be heated higher, such as even to 110° to 120° C., it waspreferred to heat rapidly at a point just above the transitiontemperature and then cooled quickly only to the minimum necessary forhuman body tolerance, such as 50° to 55° C., a temperature just aboutwhat was believed to be the crystalline transition point, the lowerlimit being an extreme. However, that temperature of 50° to 60° C. isquite hot, and at the very painful limit of human body tolerance,generally too hot to be comfortable and it is usually painful to mostpeople. It is now found that if the heating of the plastic above aminimum softening temperature exceeding the crystalline point of 55° to60° C. variable somewhat with the history of the plastic formation andthe heat treatment is for a period sufficient to thoroughly soften toconvert all of the crystalline substance to its amorphous form, thesespecific plastic bodies go through a hysteresis range. There will be asubstantial time delay upon cooling of these softened plastics beforethey reset to crystalline form. Thus, they may be cooled to a quitecomfortable body temperature such as down to about 40° C. or less andstill maintain their soft amorphous plastic characteristic for areasonable time to slowly mount about the body member to be supported asa cast or splint at the then comfortable body temperature as stated. Theformed splint placed about the body member may be held in that positioneven for a significant additional time period of 5 to 10 minutes beforecrystallizing to the rigid crystalline body supporting form in the shapeinto which it was deformed. A cooling curve illustrating the hysteresisis shown in FIG. 10.

In my prior copending application, Ser. No. 683,016, now U.S. Pat. No.3,490,444, the tendency of these sheet and tape materials to develop acreep or plastic flow over substantial prolonged periods of use when soemplaced as a body member support was discovered, which is undesirablein body splint, cast or other body support member. Particularly in useswhere close support is needed, the support has its tendency to lose itsimmediate utility as a form setting shape.

That tendency of the support to become slightly deformed in use wasovercome by including reenforcing fiber materials in the plastic body.Such plastic was also improved by having its surface protected withadhesive coating members which may be applied with a pressure-sensitiveadhesive for subsequent removal before use, which protects the freshpolymeric support material in unoxidized, fresh, unaged condition.Various useful coatings for that purpose are described and claimed, thefurther substance of the disclosure of that parent application beinghere incorporated by reference.

According to this invention, it is found that the plastic needs only tobe heated for a period sufficient to convert all the crystallinesubstances to an amorphous form, and in the amorphous stage there isdeveloped a hysteresis whereby a very substantial delay will take placein returning to the crystalline form by cooling. When the plastic issoftened completely there will be a hysteresis or delay in hardening byrecrystallization sufficient not only to allow the temperature to bereduced well below the temperature at which the crystalline form isstable, whereby the cooled and softened plastic may be applied as asplint or cast at a comfortable temperature to the human body, but thehysteresis will provide sufficient time delay in the recrystallizationto allow the product to be comfortably molded about and shaped to thebody element to be supported before substantial hardening takes place.

It is now further found according to the present invention that theplastic sheet material lying flat on the surface of a body member tendsto trap moisture upon the skin of the user, which is a source ofirritation, discomfort and sometimes a source of contamination of theskin surface of the encased body member. In some types of splints suchas hand splints, the accumulated moisture provides a slimey irritatedfeeling to the user-wearer.

According to the present invention, the skin discomfort generally due tomoisture is removed or reduced by several alternate structuralmodifications in the surface and possibly also the body of the sheetmaterial.

In one modification, the surface may be made irregular whether bytexturing, knurling, cratering with half pocks pressed or cut therein,whereby the normally smooth film of moisture on the skin is interrupted.Thereby, any liquid may seep into the surface irregularities to avoidformation on the skin of the continuous uncomfortable slimey film.

When the sheet has been reenforced with fiber so that perforation willnot substantially destroy the inherent strength of the sheath plastic,then it may be perforated with close set perforations to provide theadequate porosity for substantial evoluation of moisture outward throughthe plastic from the skin surface.

In a third alternate, the body of the sheet may be treated with afoaming or gas-blowing agent whereby the entire sheet of plastic willfoam when heated sufficient to soften it. In another procedure, one orboth surfaces of the plastic are treated with a foaming agent such as bywetting the surface with a solvent, whereby upon subsequent heating tosoften the sheet it develops a surface porosity or foam. Such surfaceporosity besides allowing escape of evolving moisture from the skinsurface of the encased body member into the pores of the porous texture,also provides a comforting resiliency or softness against the skin ofthe body member which better conforms the support to the shape of thebody member while also providing a softening, skin comfortingencasement. Nevertheless, such plastic sheet is foamed, softened and setin foamed condition about the body member, whereby it provides both theabsorption and/or allows escape of skin moisture and the adequatestrength needed for splint reenforcement of the body member thusencased.

The invention is further described with reference to the drawingswherein:

FIG. 1 shows the plastic support as sheet material formed with surfaceirregularities consisting of cup-like craters formed therein;

FIG. 2 shows a similar sheet material wherein the surface irregularitiesare knurlings;

FIG. 3 shows the same sheet material wherein the surface is textured;

FIG. 4 illustrates fiber-reenforced plastic sheet having closeperforations cut entirely through the thickness thereof;

FIG. 5 illustrates the plastic sheet having one surface foamed;

FIG. 6 illustrates the same plastic sheet wherein the entire body hasbeen homogeneously foamed;

FIG. 7 illustrates a sheet in which only both opposite surfaces of thesheet are foamed;

FIG. 8 illustrates a sheet wherein the foamed pores are interconnected;

FIG. 9 illustrates that these plastic substances will merely soften withheat and crystallize with cooling; and

FIG. 10 illustrates the hysteresis of a cooling curve.

As shown in the drawings of FIGS. 1, 2 or 3, the surface 12 of the sheet10 has cup-like craters 14 impressed into the softened surface, eachdepression forming a cavity in which moisture in contact with the skinsurface will accumulate, providing both an air space and cavities toaccept and store exuded moisture from the skin surface. The cup-likecavities are quite closely spaced, usually less than one quarter oncenter to provide optimum moisture storage capacity.

The application of the same moisture storage principle is shown in thestructures of FIGS. 2 and 3. In FIG. 2 the sheet 10 has knurlings 16 cutinto the surface 12 which provide grooved cavities which can occlude andstore the slimey moisture. FIG. 3 provides a roughened surface 18referred to as textured, generally formed by blowing fine, needle-likeblasts of air evenly over the surface and which penetrate the softenedsurface sufficient to provide the moisture storage surfaceirregularities. A similar effect of texturing can be obtained by othermethods such as pressing the softened plastic against a desirably-shapedsurface such as coarse woven cloth which itself may be formed ofstiffened fiber to create negative fibrous impressions within the softplastic surface.

As shown in FIG. 4, the plastic sheet 10 can be perforated with closelyspaced perforations 20. The closely spaced perforations are spaced from1/16 to 1/4 inch apart and tend correspondingly to weaken the plasticsheet so that in this instance the plastic sheet will be fiberreenforced by fibers 22 incorporated within the fiber sheet, sufficientto provide the extra strength to allow the body to be perforated withperforations from about 1 to 10 percent of the volume of the body 10.

Another desirable form of surface irregularity is to provide body poresin the sheet, such as by foaming. The foam or cellular surface is asofter resilient body contour-conforming surface which provides airspaces extending progressively from the surface in contact with the skininward of the plastic sheet to allow absorption of moisture and a softersurface texture. Merely foaming to provide gas spaces 24 in one surfaceof the sheet 10, as shown in FIG. 5, may be adequate for much of thisfunction. However, as shown in FIG. 7, it is sometimes commercially morefeasible to foam both sides of the sheet 26 and 28 by dipping thepolymer sheet in a solvent material which, upon subsequent heating,causes the dried sheet A to develop the pores in both surfaces 26 and28. The center portion 30 of the plastic body does not need to containpores and, consequently, may remain as mere sheet reenforcement.

As shown in FIG. 6, the plastic body 10 may also be formed with pores 32distributed homogeneously throughout the body. This may be done byforming the sheet as a foamed body so that its foamed texture is notmodified in any way during conversion by softening of the sheet fromsheet form to molded splint or cast form enclosing the body member.

As shown in FIG. 8, the foamed pores may be interconnected air spaces 34extending from surface to surface of the plastic so that the foamed bodyallows "breathing" to transfer moisture from the skin of the encasedbody member to the outside of the cast.

The invention is further described with respect to the examples whichillustrate the practice of this invention:

EXAMPLE I

Precipitated balata (purified natural transpolyisoprene) is blended on atwo roll mill at about 90° C. for fifteen minutes in ratio of 100 partsof polymer per 2 parts of cotten linters, 10 parts of finely-powderedtitanium dioxide and one-half part of antioxidant as described in myparent application. The sheets obtained from the mill were molded in aframe to 130 mils thickness of approximately 12 inch square dimensions.The compressed sheets were then removed from the frame and perforatedwith one-sixteenth of an inch in diameter perforations spaced a distanceof about one quarter inch, the perforations extending from surface tosurface as shown in enlarged detail in FIG. 4.

In forming the splint the sheet was dipped in a water bath for a halfminute at a temperature just below boiling, about 95° C., and heldtherein, then withdrawn and cut into a deformable pattern with a pair ofscissors to correspond to the contours of the wrist and fingers to beencased. The softened sheet was then applied about the wrist and fingersand molded into place closely about each joint and bony deformation bypressing against the body member. The contiguous cut parts of the splintwere cohered into a unit by slight pressure and all rough edges wereremoved, smoothing with slight pressure. During the formation andshaping, if a longer time is needed to effect the perfect fitting of thecast, it may be slightly rewarmed by again dipping into the hot waterbath or locally heated with a warm surface or a jet of hot air. Theemplaced and formed cast will set merely by holding the hand with thecast thereon quiescent for fifteen to thirty minutes, but the settingprocess can be accelerated by dipping the encased member in ice water.It is to be noted that the sheets can be deformed over joints bymanually working with applied pressure to fit closely about the contoursof bony projections, etc., and after having set with cooling to bodytemperature, this splint was found to be dimensionally stable, and closefitting, without irritation of bony projections typical of the hand andwrist for as long as in use. After completion and setting of the splint,undesirable edges resulting from cutting may be softened by warming thesplint edges only and then manually smoothing. The splint is sopermanent that it can be used for years and it is easily applied toarthritic patients where the splint may need to be fitted about aswollen hand bone projection with a good, close and delicate fit. Thissplint is more comfortable in the ability to transfer moisture throughthe close perforations, avoiding a wet clammy feeling about the encasedbody member while still retaining its functional body member supportingstrength.

EXAMPLE II

The sheet of Example I, instead of being perforated, was knurled to formdepressions in the surface of about one-thirty second of an inch depthto a surface covering as shown somewhat exaggeratedly in FIG. 2. Thissheet, too, showed greatly improved comfort over a sheet having acontinuous flat surface. The present example was repeated, except thatthe pattern was changed by impressing cups rather than knurlings asshown in FIG. 1. In a third experimental run the surface was textured asshown in FIG. 3 to produce a roughened fiber-like effect as irregularityupon the surface, again to a depth of about one-thirty second of aninch, insufficient to significantly reduce the strength of the originalsheet.

EXAMPLE III

The sheets as formed in Example I are immersed in n-hexane ether for aperiod of fifteen minutes, withdrawn and allowed to dry in air. Theproducts are then packaged and ready for use. Upon use the sheet iswarmed in a pan of warm water at a temperature of about 85° to 100° C.and the sheet softens and simultaneously develops a foamed surface onboth sides. The foam has not homogeneously penetrated into the center, astructure illustrated in FIG. 7. In its softened condition the foamedsheet is wrapped about the body member of the patient and, upon cooling,will set to a strong cast and moisture absorptive body support member ofgreat comfort and security to the user.

Following the procedure of this Example, various solvents such asliquified petroleum gases, acetone and halogenated gases may be used assolvent, selected to avoid excessive solubility in substitution for then-hexane, varying the temperature of the solution to adjust for theparticular solubility of the plastic therein and simultaneously varyingthe time of immersion somewhat, merely to allow absorption of sufficientsolvent in the polymer to provide for subsequent foaming upon heating.Such solvent, as stated, is evaporated to superficially dry the plasticsheet so that it may be stored until ready for use.

It is possible as shown in this example also to coat only one surface ofthe plastic by applying the solvent through rollers wet with thesolvent, handling the plastic in continuous sheet form while maintainingthe surface substantially wet by a series of rollers for a correspondingperiod of time. When only one surface of the sheet has been thus treatedwith solvent, upon subsequent warming of the sheet plastic only thattreated surface will expand to porous form structure as shown in FIG. 5.

EXAMPLE IV

In a modified form as shown in FIGS. 6 and 8, the plastic in the liquidform can have a gas incorporated under high pressure and cast under highpressure with the gas trapped therein. Upon subsequent warming the sheetwill expand to provide a homogeneous porous interior. It is possiblethat the warm gas-containing plastic can be cast in sheets of desiredthickness and in porous form so that upon subsequent warming they do notfoam or change in dimension in any way, since the foamed condition isalready present in the sheets as they are distributed.

EXAMPLE V

Sheets as formed in Example I are soaked for two days in a saturatedaqueous solution of ammonium carbonate in a closed container. They arethen removed and warmed in a hot air oven using a thin glycerol layer toprevent sticking; and heated at 90° C. 760 Torr for twenty minutes.Randomly shaped and sized surface indentations are found to result onthe upper side, providing modified surface texturing. The face of thesheet splints thus formed with their surface adjacent to the skin doesnot have the uncomfortable characteristics due to a slimey moistureaccumulation as described above.

EXAMPLE VI

In a modified form as shown in FIGS. 6-8, the plastic sheet is soakedfor one half hour or longer in methanol and then superficially dried bywiping. The sheets are then warmed at 90° C. for two minutes in aglycerol bath. The pressure is then reduced to less than 10 mm Torr at90° C. for ten minutes. The sheets are then cooled at atmosphericpressure. The resultant product had about one hundred porous openings inthe surface per square inch of surface and provided direct void channelsbetween the surfaces. Repetition of soaking and evaporation increasesthe porosity at a controllable rate. The resulting open foam structurecan be softened by warming in water near the boiling point and formedinto a rugged cast about a fractured or injured body member. It can beso retained in protective support for long periods of time withoutdiscomfort due to odor or moisture collection. Areas of discomfort dueto chaffing, resulting from alterations of body contours on healing, canbe rectified by warming isolated locations with a hot surface, such as aheat sealer commonly used in plastic packaging. A wrapper splint may becut longitudinally with a common orthopedic rotary saw while cold,opened like a bivalve and converted to a removable splint withoutaltering its contour-fitting qualities. The bivalve clam-like splint canbe kept closed with exterior tapes, etc., as needed.

EXAMPLE VII

A solid sheet of plastic corresponding to that described in Example I issimilarly made except that the polymer is low temperature polymerizedpolychloroprene. The sheet in an unaged condition is then soaked forseveral days in diethyl ether and foamed, after superficial drying, byheating for ten minutes in boiling water. The resultant product has acellular structure and surface pores which improve its value as asplinting material. It is found that this product is useful for manystatic hand splints but needs external support in splints encounteringstress such as in "cock up" splints for spastic wrists. It is preferredthat the sheet for foaming be freshly prepared or that the surface beprotected as described in my copending application.

EXAMPLE VIII

Example VII is repeated with a polymer sheet made as in Example I exceptthat the plastic sheet contains fifty parts of transpolyisoprene orfifty parts of transpolychloroprene. The results obtained are similarwith the product requiring external support in certain cases asdescribed above, although the inclusion of 1/4 inch fibers in quantityof one part as in my original composition greatly increases itsstrength, making it possible to use this as a cast for large fractures.

While as stated in Example I the sheets may contain reenforcing fiber,whatever the surface configuration, and that fiber will be necessaryonly where substantial perforation is applied, the fiber can be omittedwith, however, some sacrifice of inherent strength including reducedtendency of the polymer sheet to creep when applied as a splint about abody member.

In applying the said sheet material, it may be warmed in a hot waterbath sufficient to soften it. Where the sheet material includes a gasforming agent, it becomes foamy when warmed. The warming temperatureusually is less than 110° C., but always is above the body temperatures,such as above 60° C., which is sufficient to activate the foaming agentfor developing a foam in one or both surfaces, and sometimes throughoutthe entire body of the sheet material. Such sheets may be quite thin,having a thickness as low as 2 mils, ranging upward to 200 mils.However, it is most usual for body support to use a sheet having athickness in the range of 100 to 150 mils. Upon warming, the sheetmaterial becomes softened in a few minutes, sufficient to deform theentire sheet about the body member to be encased. It may be cut with apair of scissors to the desired pattern or splint or protective cast asneeded for the particular member to be supported. It is pressed aboutthe body member for comfortable support with the surface having theirregularities or foam disposed adjacent to the skin of the body memberbeing encased. The softened edges with firm pressure will cohere to eachother, but the edges of the sheet may be slightly rewarmed as needed forimproving the adhesion after assembling the sheet about the body member,if this is found to be necessary.

Other improvements as described and claimed in my parent applicationincluding desirable coatings may be used with the surface modifiedsheets thereof.

What is claimed is:
 1. A process of forming a body supporting membersuch as a cast, splint or the like, comprising warming a sheet ofcrystalline thermoplastic polymer having a thickness in the range ofabout 2 to 200 mils, to a temperature in the range of about 60° to 110°C. for a heat softening period sufficient to convert the totalcrystalline substance to a softened, amorphous form, said heat-softenedsheet of polymer developing a hysteresis to have a setting timesubstantially delayed to remain soft and amorphous below the crystallinesetting temperature, whereby it may be cooled to a comfortable bodytemperature below about 40° C., whereby the sheet may be formed andshaped for use as a body supporting cast or splint, .[.said sheet havingat least its surface adjacent to the body member to be protecteddeformed to include surface irregularities capable of absorbing andinterrupting continuous moisture films that may be developed upon thebody member to be protected, said surface irregularities consisting ofcup-like depressions, knurled depressions, texturing, foam and closespaced perforations which are evenly distributed throughout the surfaceof the said plastic and the like,.]. cutting said softened sheet todimensional size and manually shaping, wrapping and forming said sheet.[.upon.]. .Iadd.at a comfortable body temperature in the form of.Iaddend.the body member to be supported .[.and protected at saidcomfortable body temperature with the surface irregularities disposedadjacent to the body member enclosed,.]. and maintaining the entiresupported assembly substantially immobile until the sheet sets bycrystallization to a rigid body support.
 2. A process of forming a bodysupporting member such as a cast, splint or the like, comprising warminga sheet of polymer consisting of a conjugated diolefine compound havinga thickness in the range of about 2 to 200 mils, setting bycrystallization at temperatures below about .[.50° C..]. .Iadd.40°C..Iaddend.and being heat softened and pliable at raised temperatures inthe range of 60° C. to 110° C., said sheet having a hysteresis wherebyit may be cooled substantially below its normal crystallization point,to lower temperature in a comfortable contact with a body member at atemperature below about 40° C., whereby it may be heat softened,deformed and shaped for use as a body supporting medical cast or splint,said sheet having at least its surface adjacent to the body member to beprotected deformed to include surface irregularities capable ofabsorbing and interrupting continuous moisture films that may bedeveloped upon the body member to be protected, said surfaceirregularities consisting of cup-like depressions, knurled depressions,texturing, foam and .[.closed space.]. perforations which are evenlydistributed throughout the surface of said plastic and the like, cuttingsaid softened sheet to dimensional size and manually shaping, wrappingand forming said sheet upon the body member to be supported andprotected at said comfortable body temperature with the surfaceirregularities disposed adjacent to the body member .[.enclosed.]., andmaintaining the entire supported assembly substantially immobile untilthe sheet sets by crystallization to a rigid body support.
 3. A processof forming a body supporting member such as a cast, splint or the like,comprising warming a sheet of crystalline thermoplastic polymer selectedfrom the group consisting of transpolyisoprene and transpolychloroprenehaving a thickness in the range of about 2 to 200 mils, to a temperaturein the range of about 60° C. to 110° C. for a heat softening periodsufficient to convert the total crystalline substance to a softenedamorphous form, said heat softened sheet of polymer developing ahysteresis to have a setting time substantially delayed to remain softand amorphous well below the crystalline setting temperature, whereby itmay be cooled to a comfortable body temperature without immediatelysetting, cooling said heat softened plastic sheet to a comfortable bodytemperature below about 40° C., whereby the sheet may be formed andshaped for use as a body supporting cast or splint, said sheet having atleast its surface adjacent to the body member to be protected deformedto include surface irregularities capable of absorbing and interruptingcontinuous moisture films that may be developed upon the body member tobe protected, said surface irregularities consisting of cup-likedepressions, knurled depressions, texturing, foam and close spacedperforations which are .[.evenly.]. distributed throughout the surfaceof said plastic and the like, cutting said softened sheet to dimensionalsize and manually shaping, wrapping and forming said sheet upon the bodymember to be supported and protected at said comfortable bodytemperature with the surface irregularities disposed adjacent to thebody member .[.enclosed.]., and maintaining the entire supportedassembly substantially immobile until the sheet sets by crystallizationto a rigid body support.
 4. The process as defined in claim 2 whereinthe sheet material has surface irregularities comprising a foamy textureformed by generation of gases in the sheet material adjacent to at leastone surface prior to applying said sheet material to the body member tobe supported.
 5. The process as defined in claim 2 wherein the surfaceirregularities comprise foam formed by generation of gases extendingthroughout the body of said sheet material from surface to surface priorto applying said sheet material to the body member to be supported. 6.The process as defined in claim 2 wherein the sheet material includes afoaming agent activatable with heat so that upon warming said sheetmaterial for softening sufficient to apply the said material as a bodysupport member the foaming agent is simultaneously activated to convertat least one surface of the sheet material to a foamy mixture prior toapplying said sheet material to the body member to be supported.